1. Field of the Invention
This invention relates to a photosensitive resin composition used for forming fine patterns in microelectronic devices such as semiconductor devices, magnetic bubble devices, optoelectronic devices and a method for forming fine patterns with said composition.
2. Brief Description of the Prior Art
There is a tendency that semiconductor integrated circuits become higher in their packing densities from year to year. Therefore, their pattern lines become finer and finer. Thus, fine patterns must be formed using high resolution resists.
Fine patterns are produced by (a) X-ray lithography, (b) electron beam lithography or (c) photo lithography.
However, practical X-ray sources have not been developed for X-ray lithography and the electron beam lithography requires a long time for drawing the patterns on resist coated on a substrate.
Photo lithography uses negative type photoresists or positive type photoresists as resists. The negative type photoresists include (a) those which comprise a hydroxystyrene polymer and an aromatic monoazide compound. However, in the case of said photoresists (a) the azide compound used is a solid of high crystallinity and this is precipitated from solution or precipitated from coating film when the resists are made into a coating film. Furthermore, the crystals remain as fine particles in unexposed portions which are to be dissolved upon development with an alkaline aqueous solution and the remaining crystals cause closing up of patterns or disruption of patterns.
Other representative negative type photoresists are compositions comprising combinations of cyclized rubbers and aromatic azide compounds. As the aromatic azide compounds, there have been used azidobenzal ketones such as 2,6-bis(4'-azidobenzal)-4-methylcyclohexanone and 2,6-bis(4'-azidobenzal)cyclohexanone.
The maximum absorption wavelength region of these negative type photoresistors is 360 nm corresponding to the aromatic azide compounds used and since in this region there occur conspicuous interference and diffraction of light, resolution of photoresists is limited to 1.5 .mu.m. If materials sensitive in shorter wavelength region are found, the resolution of photoresists is increased. Furthermore, in the case of said negative type photoresists comprising cyclized rubbers and aromatic azide compounds, developing solution which dissolve uncured portions swell the cured resist at the time of development after curing with UV rays and thus cause expansion or winding of the resist. It is considered that the swelling of the resist per se in addition to the interference and diffraction of light is a big factor for reduction of resolution.
On the other hand, representatives of positive type photoresists are those which comprise combinations of novolak resins and quinonediazide compounds and o-naphthoquinonediazide and some modified ones of these are used as photosensitive materials.
Positive type photoresists are generally superior in resolution and this is considered because the base resin used is an organic substance such as novolak resin while the developing solution is an alkaline aqueous solution and therefore the resin portion does not swell at the time of development and only the portion exposed to UV rays is dissolved. However, the conventional positive type photoresists have the defects that the maximum absorption wavelength region thereof is 340-450 nm like that of negative type photoresists for obtaining high sensitivity and so they are liable to show reduction in resolution due to interference or diffraction of light.